The invention relates to improvements in apparatus for separating solid and liquid fractions in a mixture of such fractions. More particularly, the invention relates to improvements in filtering apparatus which can continuously separate solid fractions (e.g., impurities) from liquid fractions in mixtures of solid and liquid fractions.
German patent application No. 36 14 688 A1 of Ragnegard (published Dec. 18, 1986) discloses a filtering apparatus wherein a cylindrical vessel confines a plurality of filters which are rotatable by a driven shaft and define internal chambers for the separated liquid fraction of a mixture in the vessel. The solid fraction is intercepted by the filters, and the thus intercepted solid fraction is removed and evacuated by devices which are installed in the vessel adjacent the external surfaces of foraminous portions of the filters. The lower half of the vessel contains a mixture of solid and liquid fractions, and such mixture is maintained at a pressure above the pressure in the chambers of the rotary filters so that the liquid fraction is induced to flow into the filters with attendant interception of solid fraction at the external surfaces of the filters. The .devices which serve to evacuate the intercepted solid fraction are installed in the vessel above the upper level of the mixture of solid and liquid fractions. This is intended to simplify the expulsion or withdrawal of intercepted solid fraction from the interior of the vessel. The apparatus of Ragnegard exhibits the drawback that only a relatively small portion of each filter is used to segregate solid fraction from liquid fraction because the upper half of the vessel and hence the upper part of each filter in the vessel, is disposed at a level above the mixture of solid and liquid fractions. Therefore, and if the apparatus of Ragnegard is to be used to filter large quantities of a mixture of solid and liquid particles per unit of time, the dimensions of the vessel and of the filters must be increased accordingly. Alternatively, it is necessary to employ two or more relatively small filtering apparatus.